This invention generally relates to a method and system for radio frequency communication, and more particularly, to a method and system for autonomous two-way radio frequency communication between at least one first station and a second station.
In the launch vehicle industry, radio frequency (RF) telemetry signals are transmitted from the launch vehicle to one or more ground, sea, air, or space-based receiving or tracking stations to thereby indicate data on the performance, health, and status of various monitored parameters of the launch vehicle to launch personnel. In this regard, closure of the one-way RF telemetry link between the launch vehicle and the receiving or tracking station is typically accomplished by using brute-force methods. Such methods include high power transmitters and omni-directional antennas on the launch vehicle, pre-launch software coding to control the launch vehicle antenna steering and transmit antenna selection during the mission, and low telemetry data modulation rates.
For example, an omni-antenna provides line-of-sight coverage over a broad range of angles off of the antenna bore sight. An omni-directional design allows a combined two antenna arrangement to cover most of 360xc2x0 laterally around a launch vehicle. However, the peak gain performance of omni-antennas is very low, typically around 5 db, and provides minimum coverage towards the nose and tail of a launch vehicle. In addition, the design assumes a minimum gain over 95% of the surface of the transmit antenna radiation sphere. This gain number, typically on the order of xe2x88x9213 db for S-Band frequencies, is then used to predict the communication link margin performance and drive the requirements of the other telemetry system components. An over-designed method such as this can drive overall cost of the system by requiring higher power transmitters and reductions in allowable data transmission rates. This lower antenna gain approach may result in earlier loss of the telemetry signal from the launch vehicle in the case of a launch anomaly or a non-nominal trajectory.
One major consideration in the efforts to maintain a communication link is that the pointing angle between the launch vehicle transmit antennas and the tracking station receive antennas varies continuously throughout the mission. For example, in the launch vehicle industry, most RF signals require line-of-sight geometry between the tracking station receive antenna and the launch vehicle transmit antenna to process the RF signal. However, ensuring that line-of-sight geometry is maintained throughout the mission is extremely difficult, especially during anomalous or non-predicted launch vehicle trajectories and orientations.
Accordingly, it is an object of the present invention to provide a method and system for autonomous two-way radio frequency communication.
It is another object of the present invention to provide a method and system for autonomous two-way radio frequency communication between at least one first station, such as a tracking station, and a second station, such as a launch vehicle.
It is a further object of the present invention to provide a method and system for autonomous two-way radio frequency communication that minimizes pre-flight analysis, pre-planning, and software coding efforts.
It is still another object of the present invention to provide a method and system for autonomous two-way radio frequency communication that maximizes telemetry data reception by a tracking station for the maximum time possible during a launch vehicle mission.
It is yet another object of the present invention to provide a method and system for autonomous two-way radio frequency communication that can transmit more telemetry data at higher transmission rates over existing systems.
The present invention achieves one or more of these objects by providing a method and system for autonomous two-way radio frequency communication between at least one receiving or tracking station (e.g., a first station) and a launch vehicle (e.g., a second station). Generally, in one aspect of the present invention, the two-way radio frequency communication system includes the second station which may receive unique RF signals in at least first and second antennas, or, in three, four, five, six, or any number of additional antennas (or antenna elements) that are positioned on the second station. A processor determines which of the first and second antennas, and any additional antennas, has the higher signal strength. A transmitter, located on the second station, is adapted to transmit telemetry signals over the antenna that received the unique RF signal that had the higher signal strength.
The telemetry signals contain data on monitored parameters of the launch vehicle. Once transmitted by the transmitter via the connected antenna, the telemetry signals may be received in the one or more first stations that transmitted the unique RF signals to the second station. Throughout the launch vehicle mission the transmitter output signal is repeatedly switched to the particular antenna that currently is receiving the unique RF signal having the higher signal strength, which is at that moment the best RF communication link between the first station and the second station. Thus, the peak gain of that particular launch vehicle antenna at that moment is more aligned with the peak gain of the first station receiving antenna. Selecting the antenna with the higher signal strength as the transmit antenna helps ensure that the telemetry signals transmitted are more likely to be received in the first station for evaluation by launch personnel.
In another aspect of the two-way radio frequency communication system, the system includes the second station which may receive unique RF signals in at least a first receive antenna, or, in two, three, four, five, six, or any number of additional receive antennas that are positioned on the second station. The receive antennas in this embodiment are adapted to scan for and receive the unique RF signals transmitted from the one or more first stations. A phased array antenna would be an example of such an antenna.
A processor determines which of the receive phased array antennas has the best quality signal vector, which is an indication of the best RF communication link between the first station and the second station. A transmitter located on the second station is adapted to radiate telemetry signals over at least a first transmit antenna to the first station along a path parallel to the best quality signal vector. Such a first transmit antenna may also be a phased array antenna. There may be two, three, four, or any number of transmit phased array antennas located on the second station. Transmitting telemetry data along a path parallel to the best quality signal vector helps ensure that the telemetry signals transmitted by the transmitter via the connected transmit phased array antenna are more likely to be received in the first station for evaluation by launch personnel.
Generally, in one aspect of the two-way radio frequency communication method of the present invention, the method includes the steps of transmitting a unique RF signal from a first station, receiving the unique RF signal with at least first and second antennas on the second station, determining a first signal strength for the unique RF signal received in the first antenna, determining a second signal strength for the unique RF signal received in the second antenna, determining which of the first and second signal strengths is higher, connecting a transmitter on the second station to whichever first or second antenna received the unique RF signal with the higher signal strength, and transmitting with the transmitter a first telemetry signal containing monitored parameters of the second station over the connected first or second antenna.
For purposes of facilitating communication, and otherwise avoiding loss of the RF telemetry link, in one embodiment of the method of the present invention, the radio frequency signals are transmitted from at least one ground station and at least one non-ground station. Telemetry signals transmitted from the launch vehicle may be received in either or both of the at least one ground station or the at least one non-ground station. Thus, as the second station moves along its mission path in relationship to the at least one ground station and the at least one non-ground station, the method of the present invention continually selects the antenna on the second station for transmitting telemetry data that has the best RF communication link to one or the other of the at least one ground station or the at least one non-ground station.
In another embodiment of the method of the present invention, the step of connecting the transmitter to the first or second antenna includes an optimizing step of applying a smoothing algorithm, which is executed within a processor. The smoothing algorithm inhibits switching between the first and second antennas if the change in the higher signal strength between the first and second antennas is less than a selected absolute change amount. This inhibits rapid and unnecessary switching between antennas.